Primer compositions

ABSTRACT

A primer composition usable for steel sheets and plastic sheets in vehicle bodies consists essentially of a component (A) consisting essentially of at least one resin having a glass transition temperature of not higher than -20° C., preferably not lower than -75° C., and an elongation at break of not less than 400% preferably not greater than 900%, at 20° C. and a component (B) consisting essentially of at least one crosslinking resin, the weight ratio of solid content of (A) to (B) being 70-99:30-1.

This is a division of application Ser. No. 07/197,149 filed May 23, 1988now U.S. Pat. No. 4,985,500, which in turn is a continuation of Ser. No.07/003,238 filed Jan. 14, 1987, now U.S. Pat. No. 4,830,778.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a primer composition adaptable for both steelsheet and plastic sheet as vehicle bodies.

2. Related Art Statement

Lately, the use of plastic materials for automotive parts has rapidlyprogressed since it can reduce the weight of the vehicle body, act as arust-preventing means and increase freedom of design in the automobileindustry. Moreover, the vehicle body is typically formed by intricatelycombining steel sheet with plastic sheet.

In this case, there has hitherto been adopted a method wherein thepainting of all the materials is first performed and then the paintedmaterials are assembled in a final step.

The steel sheet is degreased and phosphated to form a phosphate layerthereon. After an under coat is formed by electrodeposition, a chippingprimer or a stoneger coat is partially applied and then an intermediatecoat and a top coat are formed thereon.

On the other hand, the plastic sheet is degreased, dried and coated witha primer for the plastic sheet. Then, an exclusive intermediate coat andan exclusive top coat are successively formed thereon. In this case, theformation of the exclusive intermediate coat may be omitted.

Thereafter, the painted plastic sheet is assembled onto the paintedsteel sheet.

In another painting method, the plastic sheet is degreased, dried,coated with an exclusive primer, baked and then assembled onto the steelsheet which is previously degreased, phosphated and coated with an undercoat, and thereafter the common intermediate coat and top coat areformed and baked on the assembly of the plastic sheet and steel sheet.

According to these conventional painting methods, however, the structureof the resulting paint coats formed is different between the plasticsheet and the steel sheet and the paint used and the painting step arealso different, so that there are caused the following problems:

(1) Since the painting equipment must be separately arranged for thepainting of steel sheet and for the painting of plastic sheet, not onlythe operation efficiency is poor but also the huge equipment investmentis required;

(2) The difference in appearance such as color tone, gloss and the likeis caused between the plastic sheet and the steel sheet to degrade thecommercial value of the automobile as a whole;

(3) The difference in the durability of painted coating is causedbetween the plastic sheet and the steel sheet to detract from theappearance of the automobile over time; and

(4) When the plastic sheet is coated with the exclusive primer,assembled into the steel sheet and then the resulting assembly issubjected to a painting together, there problems (1)-(3) above are notcaused. In the selection of paints for intermediate coat and top coat,however, when a soft coating is used in compliance with the plasticsheet, the weather resistance, polishing property, solvent resistance,stain resistance and the like are degraded, and when a hard coating isused in compliance with the steel sheet, the impact resistance, chippingresistance and the like on the plastic sheet are degraded.

SUMMARY OF THE INVENTION

The present invention is directed to a primer composition consistingessentially of a component (A) consisting essentially of at least oneresin having a glass transition temperature of not higher than -20° C.and an elongation at break of not less than 400% at 20° C. and acomponent (B) consisting essentially of at least one crosslinking resin.The weight ratio as solid resin content of component (A) to component(B) is 70-99:30-1. The primer composition is applied onto an under coatformed in the case of the steel sheet, by electrodeposition and, in thecase of the plastic sheet, as a primer for plastic, whereby thesimultaneous painting of the intermediate coat and top coat as a hardcoating used for steel sheet is possible and the aforementioned problemscan be solved.

That is, the invention provides a primer composition consisting mainlyof a component (A) composed of at least one resin having a glasstransition temperature of not higher than -20° C. and an elongation atbreak of not less than 400% at 20° C. and a component (B) composed of atleast one crosslinking resin, and having a weight ratio as solid resincontent of component (A) to component (B) of 70-99:30-1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The component (A) used in the invention is selected from well-knownpolyurethane resin, polyvinyl resin, polyolefin resin, polyester resin,polyacrylic resin and linear high molecular weight elastomer composedfundamentally of their modified resin.

On the other hand, the component (B) used in the invention is selectedfrom well-known melamine resin, urea resin, polyisocyanate resin and amodified resin thereof, and may include resins capable of chemicallyreacting with the crosslinking resin, such as a reactive functionalgroup containing acrylic resin, epoxy resin, polyester resin,polyurethane resin and so on.

When the resin used as the component (A) has a glass transitiontemperature of higher than -20° C. and an elongation at break of lessthan 400% at 20° C., the flexibility of the resulting coat is poor, andthe impact resistance and chipping resistance on the plastic sheet arenot satisfied, and the chipping resistance on the steel sheet is alsopoor.

Even when the resin satisfies the conditions defined as the component(A), if only the component (A) is used, the ability to withstandheating-cooling cycles is poor when used as an overall coat comprisingan under coat, an inter (i.e., intermediate) coat and a top coat andconsiderable cracks are undesirably caused in the coating. For thisreason, the component (A) is used together with the component (B) in aweight ratio as solid resin content of component (A) to component (B) of70-99:30-1, whereby satisfactory heating-cooling cycle properties can beobtained. According to the invention, the components (A) and (B) areessential.

Since the component (B) is a crosslinking resin as mentioned above, whenthe solid content of component (B) in the primer composition exceeds 30%by weight, the flexibility of the resulting coating lowers, and thechipping resistance and impact resistance on the plastic sheet are poor,and the chipping resistance on the steel sheet is not satisfied, whilewhen it is less than 1% by weight, the crosslinking effect is poor, andthe heating-cooling cycle property is deteriorated, and cracks areproduced in the coating.

The primer composition consisting of the components (A) and (B)according to the invention may contain a pigment. As the pigment,mention may be made of inorganic and organic pigments usually used inthe paint, such as titanium dioxide, carbon black, talc, kaolin, calciumcarbonate, magnesium carbonate, barium sulfate, iron oxide, cyanineblue, quinacridone red and so on. In order to form the inter coat andtop coat by electrostatic painting, it is favorable if the resultingcoating has electrical conductivity. In this case, a conductive pigment,particularly conductive carbon black can be used, wherein the surfaceresistivity is usually suitable to be not more than 10¹⁰ Ω.cm.

In the primer composition according to the invention, it is desirablethat a ratio of pigment to components (A)+(B) is 0-2.0. When this ratioexceeds 2.0, the flexibility of the coating is poor, and the chippingresistance on the steel sheet and the chipping resistance and impactresistance at low temperature on the plastic sheet are poor.

Organic solvent is provided to uniformly dissolve the components (A) and(B) and stably store them for a long term. Suitable solvents includeorganic solvents for usual paint, such as ketones, esters, aromatics,alcohols, aliphatics and the like.

If necessary, the primer composition according to the invention may becompounded with additives for paint such as surface regulating agent,antisettle agent, heat degradation preventing agent, light degradationpreventing agent, pigment dispersing agent and the like as well as areaction catalyst for promoting the reaction.

The primer composition according to the invention may be produced by theusual paint manufacturing process or pigment dispersing process. Whenthe primer composition does not contain a pigment, it can be produced bymixing the components (A) and (B) with, if necessary, additives forpaint and organic solvent in the well-known agitating device such asdissolver to form a uniform resin solution. On the other hand, when theprimer composition contains a pigment, it can be produced by dispersingthe pigment into a part or whole of the resin in the well-known pigmentdispersing machine such as attritor, sand mill or the like and thenadding the remaining resin, organic solvent and additives for paintthereto so as to adjust the viscosity to a given value.

As a means for applying the primer composition according to theinvention, use may be made of well-known painting manners such as airspraying, electrostatic air spraying, electrostatic spray painting andthe like.

The primer composition according to the invention is simultaneouslyapplicable to the steel sheet for vehicle bodies after painting an undercoat and the plastic sheet after degreasing and drying. After theapplication of the primer composition, the primer coating is left tostand at room temperature for 1-10 minutes, or forced drying is carriedout at 80° C. for about 30 minutes. Then, inter and top coats usuallyused can be formed thereon.

Even when the primer composition is applied to both the steel sheet andplastic sheet, the painting of inter coat can be omitted, if necessary.As a paint for inter coat and top coat, there may be used paints usuallyused for the steel sheet for a vehicle body and the plastic sheet.

As the plastic material applicable to the primer composition accordingto the invention, mention may be made of ones used as a plastic forvehicle body, such as polyamide resin, polybutylene terephthalate resin,polyurethane resin, polycarbonate resin, unsaturated polyester resin,polypropylene resin, a mixture thereof, a reinforced resin thereof andthe like. However, the invention is not restricted to these resins as aplastic material.

As mentioned above, the primer composition according to the inventioncan simultaneously be applied to the steel sheet for a vehicle body andthe plastic sheet for a vehicle body owing to the presence of thecomponents (A) and (B) at a particular weight ratio, so that it ispossible to simultaneously paint the same hard inter coat and hard topcoat to both the sheets with the same painting equipment and to effectthe baking in the same baking furnace. Therefore, the uniformity ofqualities in the painted coats on both the sheets, for example,appearance qualities such as color tone, gloss and the like anddurability qualities such as weather resistance, chemical resistance andthe like can be made complete.

Further, when the primer composition according to the invention isapplied to the undercoated steel sheet, the chipping resistance,heating-cooling cycle property and the like are improved, and when it isapplied to the plastic sheet for vehicle body, the chipping resistance,heating-cooling cycle property, impact resistance and the like areimproved.

The following examples are given in illustration of the invention andare not intended as limitations thereof. In the examples, allpercentages are by weight, unless otherwise stated.

EXAMPLE 1 Production of Primer

100 g of a mixture having a compounding recipe as shown in Table 1 wasmixed in a dissolver and added with an equal mixed solution of xyleneand butyl acetate so as to adjust a spraying viscosity to 13 seconds(20° C.) as Ford cup No. 4, whereby a primer composition was produced.

EXAMPLES 2-17, COMPARATIVE EXAMPLES 1-5 Production of Primer

100 g of a mixture having a compounding recipe as shown in Table 1 wasthoroughly kneaded in a dissolver and then mixed in a paint shaker for 1hour. The resulting composition was added with an equal mixed solutionof xylene and butyl acetate so as to adjust a spraying viscosity to 13seconds (20° C.) as Ford cup No. 4.

The details of components shown in Table 1 are as follows.

Polyurethane resin varnish I:

Resin solution prepared by adding an equal mixed solution of xylene andmethyl isobutyl ketone (MIBK) to Sanprene LQ-377 (trade name, made bySanyo Chemical Industries, Ltd., elongation at break: 610%, glasstransition temperature: -35° C.) and having a solid content of 20%

Polyurethane resin varnish II:

Resin solution prepared by adding an equal mixed solution of xylene andMIBK to Sanprene LQ-X35B (trade name, made by Sanyo Chemical Industries,Ltd., elongation at break: 440%, glass transition temperature: -20° C.)and having a solid content of 20%

Polyurethane resin varnish III:

Resin solution prepared by adding an equal mixed solution of xylene andMIBK to Nipporan 2301 (trade name, made by Nippon Polyurethane IndustryCo., Ltd., elongation at break: 600%, glass transition temperature: -20°C.) and having a solid content of 15%

Polyurethane resin varnish IV:

Resin solution prepared by adding an equal mixed solution of Cellosolveacetate (trade name) and MIBK to Desmorac 2100 (trade name, made bySumitomo Bayer Urethane Co., Ltd., elongation at break: 350%, glasstransition temperature: -15° C.) and having a solid content of 15%

Ethylene-vinyl acetate copolymer resin varnish I:

Resin solution prepared by adding a mixed solution of xylene and MIBKwith a mixing ratio of 2:1 to Evaflex® 150 (trade name, made by MitsuiPolychemical Company, Ltd., elongation at break: 900%, glass transitiontemperature: -30° C.) and having a solid content of 20%

Ethylene-vinyl acetate copolymer resin varnish II:

Resin solution prepared by adding a mixed solution of xylene and MIBKwith a mixing ratio of 2:1 to Evaflex® 410 (trade name, made by MitsuiPolychemical Company, Ltd., elongation at break: 300%, glass transitiontemperature: -20° C.) and having a solid content of 15%

Ethylene-vinyl acetate copolymer resin varnish III:

Resin solution prepared by adding an equal mixed solution of toluene andxylene to MB-600 (trade name, made by Nippon Unicar Co., Ltd.,elongation at break: 880%, glass transition temperature: -75° C.) andhaving a solid content of 10%

Ethylene-ethyl acrylate copolymer resin varnish:

Resin solution prepared by adding an equal mixed solution of toluene andxylene to MB-870 (trade name, made by Nippon Unicar Co., Ltd.,elongation at break: 800%, glass transition temperature: -75° C.) andhaving a solid content of 10%

Polyolefin resin varnish:

Resin solution prepared by adding toluene to Unistol P (trade name, madeby Mitsui Petrochemical Industries, Ltd., elongation at break: 500%,glass transition temperature: -40° C.) and having a solid content of 7%

Chlorinated ethylene-vinyl acetate copolymer resin varnish:

Resin solution prepared by adding an equal mixed solution of toluene andxylene to Superchlon BX (trade name, made by Sanyo-Kokusaku Pulp Co.,Ltd., elongation at break: 600%, glass transition temperature: -50° C.)and having a solid content of 15%

Polyisocyanate resin varnish:

Coronate HL (trade name, made by Nippon Polyurethane Industry Co., Ltd.,solid content: 75%)

Block isocyanate resin varnish:

TPKL-5-2544 (trade name, made by Sumitomo Bayer Urethane Co., Ltd.,solid content: 75%)

n-Butylated urea resin varnish:

Super Bekamin P-138 (trade name, made by Dainipon Ink and Chemicals,Inc., solid content: 60%)

Isobutylated melamine resin varnish:

Yuban 60R (trade name, made by Mitsui Toatsu Chemicals, Inc., solidcontent: 50%)

Titanium dioxide:

JR-602 (trade name, made by Teikoku Kako Co., Ltd.)

Carbon black:

Rarben 420 (trade name, made by Columbian Carbon, Japan)

Conductive carbon black:

Vulcan XC-72 (trade name, made by Cabot Corp.)

Calcium carbonate:

Homokal D (trade name, made by Shiraishi Kogyo K.K.)

Painting of steel sheet

A cold rolled steel sheet of 0.8 mm×70 mm ×150 mm was subjected to aphosphating treatment with Bonderite #3004 (trade name, made by NihonParkerizing Co., Ltd.), coated with a cation electropaint of Aqua No.4100 (trade name, made by Nippon Oil and Fats Co., Ltd.) as an undercoat, and then dried by baking at 175° C. for 20 minutes. The driedthickness of the resulting electrocoating was 20 μm.

Then, each of the aforementioned primer compositions was applied by anair spray painting process, and thereafter Epico No. 1500 Sealer TX-100(trade name, made by Nippon Oil and Fats Co., Ltd.) was applied as anamino/oil-free polyester resin series inter coat of wet-on-wet system byan air spray painting process and dried by baking at 140° C. for 30minutes. The dried thickness of the primer was 5-8 μm, and that of theinter coat was 30-35 μm.

Next, an amino/alkyd resin series solid color of Melami No. 1 Red (tradename, made by Nippon Oil and Fats Co., Ltd.) was applied as a top coatby an air spray painting process and dried by baking at 140° C. for 30minutes. The dried thickness of the top coat was 40 μm.

Painting of plastic sheet

I. Plastic sheet

(A) Polyamide resin sheet (PA) 1014RX-109 (trade name, made by UbeIndustries, Ltd.)

(B) Polybutylene terephthalate resin sheet (PBT) 5201X11 (trade name,made by Toray Industries, Inc.)

(C) Unsaturated polyester resin sheet (SMC) N12 (trade name, made byTakeda Chemical Industries, Ltd.)

(D) Polyurethane resin sheet (PU) C1056/FA720 (trade name, made byNippon Polyurethane Industry Co., Ltd.)

(E) Polycarbonate resin sheet (PC) Yupiron MB-2201 (trade name, made byMitsubishi Gas Chemical Company, Inc.)

II. Painting process

Each of the above plastic sheets having a size of 3 mm×70 mm×150 mm wasdegreased with a vapor of 1,1,1-trichloroethane (74° C.) for 60 seconds,dried, coated with the aforementioned primer by an air spray paintingprocess, and then coated with Epico No. 1500 Sealer TX-100 as anamino/oil free polyester resin series inter coat of wet-on-wet system byan air spray painting process, which was then dried by baking at 140° C.for 30 minutes. The dried thickness of the primer was 5-8 μm, and thatof the inter coat was 30-35 μm. Thereafter, the amino/alkyd resin paintof Melami No. 1 Red was applied as a top coat by an air spray paintingprocess and dried by baking at 140° C. for 30 minutes. The driedthickness of the top coat was 40 μm.

COMPARATIVE EXAMPLE 6

The same procedure as described in Example 1 was repeated except thatthe application of the primer composition was omitted.

COMPARATIVE EXAMPLE 7

The same procedure as described in Example 2 was repeated except thatPlagloss No. 3000 Red (trade name, made by Nippon Oil and Fats Co.,Ltd.) as a top coat grade for bumper was applied as a top coat by an airspray painting process instead of Melami No. 1 Red and dried by bakingat 120° C. for 30 minutes. The dried thickness of the top coat was 40μm.

                                      TABLE 1                                     __________________________________________________________________________                      Elongation                                                                          Glass                                                                   at break                                                                            transition                                                                           Example                                        Primer composition                                                                              20° C.                                                                       temperature                                                                          1    2     3    4    5     6                   __________________________________________________________________________    Component (A)                                                                 polyurethane resin varnish I                                                                    660%  -35° C.                                                                       95.5 78.0  65.9 71.4 83.0  78.0                polyurethane resin varnish II                                                                   440%  -20° C.                                        polyurethane resin varnish III                                                                  600%  -20° C.                                        polyurethane resin varnish IV                                                                   350%  -15° C.                                        ethylene-vinyl acetate                                                                          900%  -30° C.                                        copolymer resin varnish I                                                     ethylene-vinyl acetate                                                                          300%  -20° C.                                        copolymer resin varnish II                                                    ethylene-vinyl acetate                                                                          880%  -75° C.                                        copolymer resin varnish III                                                   ethylene-ethyl acrylate                                                                         800%  -75° C.                                        coplymer resin varnish                                                        polyolefin resin varnish                                                                        500%  -40° C.                                        chlorinated ethylene-vinyl                                                                      600%  -50° C.                                        acetate copolymer resin varnish                                               Component (B)                                                                 polyisocyanate resin varnish                              3.7                 block isocyanate resin varnish 4.5  3.7   3.1  8.2  0.2                       n-butylated urea resin varnish                                                isobutylated melamine resin varnish                                           Pigment                                                                       titanium dioxide                    18.2  15.8 20.4 15.8  18.2                carbon black                        0.1   0.2             0.1                 conductive carbon black                             1.0                       calcium carbonate                         15.0                                component (A)/component (B)    85/15                                                                              85/15 85/15                                                                              70/30                                                                              99.1  85/15               pigment/components (A) + (B)   0    1.0   2.0  1.0  1.0   1.0                 Paint for top coat             Melami                                                                             Melami                                                                              Melami                                                                             Melami                                                                             Melami                                                                              Melami                                             No. 1                                                                              No. 1 No. 1                                                                              No. 1                                                                              No. 1 No. 1                                              Red  Red   Red  Red  Red   Red                 __________________________________________________________________________                      Example                                                     Primer composition                                                                              7    8    9    10   11   12   13   14   15                  __________________________________________________________________________    Component (A)                                                                 polyurethane resin varnish I                                                                    77.3 76.6 39.0 77.0                                         polyurethane resin varnish II                                                                             39.0      78                                      polyurethane resin varnish III             82.5                               polyurethane resin varnish IV                                                 ethylene-vinyl acetate                                                        copolymer resin varnish I                       78.0                          ethylene-vinyl acetate                                                        copolymer resin varnish II                                                    ethylene-vinyl acetate                                                        copolymer resin varnish III                          87.6                     ethylene-ethyl acrylate                                   87.6                coplymer resin varnish                                                        polyolefin resin varnish                                                      chlorinated ethylene-vinyl                                                    acetate copolymer resin varnish                                               Component (B)                                                                 polyisocyanate resin varnish                                                  block isocyanate resin varnish                                                                            3.7       3.7  2.9  3.7  2.1  2.1                 n-butylated urea resin varnish                                                                  4.5            3.0                                          isobutylated melamine resin varnish                                                                  5.4       1.8                                          Pigment                                                                       titanium dioxide  18.2 17.5 18.2 18.1 18.2 14.6 18.3 9.3  10.3                carbon black           0.5  0.1  0.1  0.1                                     conductive carbon black                              1.0                      calcium carbonate                                                             component (A)/component (B)                                                                     85/15                                                                              85/15                                                                              85/15                                                                              85/15                                                                              85/15                                                                              85/15                                                                              85/15                                                                              85/15                                                                              85/15               pigment/components (A) + (B)                                                                    1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0                 Paint for top coat                                                                              Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No.                                                                                No. 1                                 Red  Red  Red  Red  Red  Red  Red  Red  Red                 __________________________________________________________________________                      Example   Comparative Example                               Primer composition                                                                              16   17   1    2    3     4   5    6    7                   __________________________________________________________________________    Component (A)                                                                 polyurethane resin varnish I                                                                              68.9 83.3 63.9                78.0                polyurethane resin varnish II                                                 polyurethane resin varnish III                                                polyurethane resin varnish IV              82.5                               ethylene-vinyl acetate                                                        copolymer resin varnish I                                                     ethylene-vinyl acetate                                                        copolymer resin varnish II                      82.5                          ethylene-vinyl acetate                                                        copolymer resin varnish III                                                   ethylene-ethyl acrylate                                                       coplymer resin varnish                                                        polyolefin resin varnish                                                                        91.0                                                        chlorinated ethylene-vinyl                                                                           82.5                                                   acetate copolymer resin varnish                                               Component (B)                                                                 polyisocyanate resin varnish                                                  block isocyanate resin varnish                                                                  1.5  2.9  9.9       3.0  2.9  2.9       3.7                 n-butylated urea resin varnish                                                isobutylated melamine resin varnish                                           Pigment                                                                       titanium dioxide  7.5  14.0 20.0 16.7 30.0 14.6 14.5      18.2                carbon black           0.6  1.2                 0.1       0.1                 conductive carbon black               3.1                                     calcium carbonate                                                             component (A)/component (B)                                                                     85/15                                                                              85/15                                                                              65/35                                                                              100/0                                                                              85/15                                                                              85/15                                                                              85/15     85/15               pigment/components (A) + (B)                                                                    1.0  1.0  1.0  1.0  2.2  1.0  1.0       1.0                 Paint for top coat                                                                              Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Melami                                                                             Plagloss                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No. 1                                                                              No.                                                                                No. 3000                              Red  Red  Red  Red  Red  Red  Red  Red  Red                 __________________________________________________________________________

The following tests were made with respect to the coatings on the steelsheet and plastic sheet to obtain results as shown in the followingTable 2.

Test and evaluation methods

1. Chipping resistance

Testing machine:

gravelometer made by Suga Shikenki K.K.

Testing stone:

No. 7 hard pulverized sand (diameter: 2-3 mm) 100 g/test

Air pressure blown: 4 kg/cm²

Blowing angle: 90°

Sheet temperature: 20° C.

The test was made under the above conditions to evaluate the peelingstate of the coating (CP-I) and the number of rusting points generated(CP-II).

Evaluation standard of CP-I:

Peeling diameter of less than 0.5 mm, ◯ (excellent)

Peeling diameter of not less than 0.5 mm but less than 1.0 mm, Δ(acceptable)

Peeling diameter of not less than 1.0 mm, x (bad)

The evaluation of CP-II was made by the number of rusting pointsgenerated after 72 hours by spraying salt (5% salt water, temperature:35° C.) to the test sheet.

Rust number of less than 20, ◯ (excellent)

Rust number of not less than 20 but less than 50, Δ (acceptable)

Rust number of not less than 50, x (bad)

2. Heating-cooling cycle property

A cross cut of 50 mm×50 mm was formed on the test sheet, which wassubjected to a cycle of heating at 50° C. and 95% RH for 16hours→cooling at 20° C. for 0.5 hour→cooling at -40° C. for 3hours→cooling at 20° C. for 1 hour→heating at 80° C. for 3 hours→coolingat 20° C. for 0.5 hour three times to evaluate the presence of cracks inthe coating.

The evaluation standard was as follows.

Absence of crack ◯ (excellent)

Presence of cracks x (bad)

3. Gasoline resistance

The test sheet was immersed in gasoline for 1 hour to evaluate colorchange, swelling, peeling and the like of the coating. The evaluationstandard was ◯ (no change; excellent), Δ (slightly change; acceptable)and x (considerably change; bad).

4. Polishing property

The test sheet was ground with an abrasive paper (#1500), rubbed withUnicon FMC-830H (trade name, made by Ishihara Sangyo Kaisha, Ltd.) as arepair abrasive, and further polished with Soft 99 Luster (trade name,made by Nitto Chemical Industry Co., Ltd.) as a polishing wax toevaluate the appearance of the coating. The evaluation standard was asfollows.

no reduction of gloss as compared with initial stage: ◯ (excellent)

slight reduction of gloss as compared with initial stage: Δ (acceptable)

considerable reduction of gloss as compared with initial stage: x (bad)

5. Impact resistance at low temperature (High-speed impact test)

A value of impact energy when a point of impact shot through the testsheet was measured by means of a high-speed impact testing machine madeby Rheometric Corporation under such conditions that a tip diameter ofimpact point was 1.6 cm (5/8 inch), a holder was 5.1 cm (2 inch) and animpact speed was 11.1 m/sec., from which a yield energy value (joule) at-40° C. was calculated.

The larger the numerical value, the better the impact resistance at lowtemperature.

                                      TABLE 2                                     __________________________________________________________________________    Test items     Example                                                        Sheet material 1   2   3   4   5   6   7   9   10  11  12  13                 __________________________________________________________________________    Steel sheet                                                                   chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      chipping resistance CP-II                                                                    ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      PA                                                                            chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      impact resistance at low                                                                     10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12        temperature (joule)                                                           PBT                                                                           chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      impact resistance at low                                                                     40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50        temperature (joule)                                                           SMC                                                                           chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      impact resistance at low                                                                     40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50        temperature (joule)                                                           PU                                                                            chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      impact resistance at low                                                                     30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40        temperature (joule)                                                           PC                                                                            chipping resistance CP-I                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      heating-cooling cycle property                                                               ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                          ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property                                                                           ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      impact resistance at low                                                                     40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50        temperature (joule)                                                           __________________________________________________________________________    Test items         Example         Comparative Example                        Sheet material     14  15  16  17  1   2   3   4   5   6   7                  __________________________________________________________________________    Steel sheet                                                                   chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           ◯                                                                     X   Δ                                                                           Δ                                                                           Δ                                                                           ◯      chipping resistance CP-II                                                                        ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     X   Δ                                                                           Δ                                                                           Δ                                                                           ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯      polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  PA                                                                            chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           Δ                                                                           Δ                                                                           X   ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     X   ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   X                  polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  impact resistance at low                                                                         10˜12                                                                       10˜12                                                                       10˜12                                                                       10˜12                                                                       ≦9                                                                         10˜12                                                                       ≦9                                                                         ≦9                                                                         ≦9                                                                         10˜12                                                                       10˜12        temperature (joule)                                                           PBT                                                                           chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           Δ                                                                           Δ                                                                           X   ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     X   ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   X                  polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  impact resistance at low                                                                         40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       ≦9                                                                         40˜50                                                                       ≦9                                                                         ≦9                                                                         ≦9                                                                         40˜50                                                                       40˜50        temperature (joule)                                                           SMC                                                                           chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     X   Δ                                                                           Δ                                                                           X   ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     X   ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   X                  polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  impact resistance at low                                                                         40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       10˜20                                                                       40˜50                                                                       10˜20                                                                       10˜20                                                                       10˜20                                                                       40˜50                                                                       40˜50        temperature (joule)                                                           PU                                                                            chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           Δ                                                                           Δ                                                                           X   ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     X   ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   X                  polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  impact resistance at low                                                                         30˜40                                                                       30˜40                                                                       30˜40                                                                       30˜40                                                                       ≦9                                                                         30˜40                                                                       ≦9                                                                         ≦9                                                                         ≦9                                                                         30˜40                                                                       30˜40        temperature (joule)                                                           PC                                                                            chipping resistance CP-I                                                                         ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     Δ                                                                           ◯                                                                     Δ                                                                           Δ                                                                           Δ                                                                           X   ◯      heating-cooling cycle property                                                                   ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   ◯                                                                     ◯                                                                     ◯                                                                     X   ◯      gasoline resistance                                                                              ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X   X                  polishing property ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     ◯                                                                     X                  impact resistance at low                                                                         40˜50                                                                       40˜50                                                                       40˜50                                                                       40˜50                                                                       ≦9                                                                         40˜50                                                                       ≦9                                                                         ≦9                                                                         ≦9                                                                         40˜50                                                                       40˜50        temperature (joule)                                                           __________________________________________________________________________

As seen from Tables 1 and 2, the use of the primer composition accordingto the invention is excellent in chipping resistance, heating-coolingcycle property, gasoline resistance and polishing property for the steelsheet and excellent in chipping resistance, heating-cooling cycleproperty, gasoline resistance, polishing property and impact resistanceat low temperature for all plastic sheets, so that it can ensure thegood balance of total film performances required as a paint forautomobiles.

On the contrary, Comparative Example 1 is poor in the chippingresistance for the steel sheet and in the chipping resistance and impactresistance at low temperature for all plastic sheets because the ratioof component (A) to component (B) is 65/35.

Since Comparative Example 2 does not use the component (B), theheating-cooling cycle property for the steel sheet and all plasticsheets is poor.

In Comparative Example 3, since the ratio of pigment to components(A)+(B) is 2.2, the chipping resistance for the steel sheet and thechipping resistance and impact resistance at low temperature for allplastic sheets are poor.

In Comparative Examples 4 and 5, the chipping resistance for the steelsheet and the chipping resistance and impact resistance at lowtemperature for all plastic sheets are poor because the component (A) ofComparative Example 4 has a glass transition temperature of higher than-20° C. and an elongation at break of less than 400% at 20° C., whilethe component (A) of Comparative Example 5 has an elongation at break ofless than 400% at 20° C.

In Comparative Example 6, the chipping resistance for the steel sheetand the chipping resistance, heating-cooling cycle property and gasolineresistance for all plastic sheets are poor because the primercomposition according to the invention is not used.

In Comparative Example 7, since the soft top coat is used instead of thehard top coat, the chipping resistance, heating-cooling cycle propertyand impact resistance at low temperature for the steel sheet and allplastic sheets are improved, but the polishing property for the steelsheet and the gasoline resistance and polishing property for all plasticsheets are poor, so that good balance of the total film performancescannot be ensured.

What is claimed is:
 1. A primer composition consisting essentially of(A)at least one resin having a glass transition temperature of not higherthan -20° C. and an elongation at break of not less than 400% at 20° C.,and being an ethylene-vinyl acetate copolymer or a chlorinatedethylene-vinyl acetate copolymer resin or a modified resin thereofcomprising high molecular weight elastomers and (B) at least onecross-linking resin selected from the group consisting of melamineresin, urea resin, polyisocyanate resin, blocked isocyanate resin andpolyurethane resin, wherein the weight ratio as a solid resin content ofcomponent (A) to component (B) is 70-99:30-1.
 2. The primer compositionof claim 1, wherein component (A) is an ethylene-vinyl acetatecopolymer.
 3. The primer composition of claim 2, wherein component (B)is a blocked isocyanate resin.
 4. The primer composition of claim 1,wherein component (A) is a chlorinated ethylene-vinyl acetate copolymer.5. The primer composition of claim 4, wherein component (B) is a blockedisocyanate resin.